1. Field of the Invention
This invention relates to electronic locks and to control circuits for such locks that operate when power fails or when the power supply voltage decreases. More specifically, this invention relates to power failure control circuits that operate to set a desired locked or unlocked status for the lock during the power failure period and to ensure proper startup and lock operation after power is restored.
2. Description of Related Art
Electronic locks are widely used in hotels, public buildings, prisons and commercial establishments as well as in high-end residential installations to provide sophisticated operational features. Such features may include electronic logging of lock operation, remote control of lock function, access authorization, indications of unauthorized break-in attempts and other lock and security related features.
Locks of this type typically include an electromechanical lock actuator to lock and unlock the door and may offer a variety of other features, including non-volatile memory storage, wired or wireless remote communication capability, such as WiFi, Bluetooth or infrared, LED indicators and/or LCD screens for signaling lock status, input devices, such as keypads, thumbprint readers, RFID or other electronic security devices for reading electronic keys and/or environmental sensors for temperature, smoke, or fire conditions.
There are many electronic lock designs, providing a variety of different features, however such electronic locks typically include a microcontroller or microprocessor (hereinafter referred to as the “microcontroller”) running a stored control program to provide the various lock functions and features. Each of the electrically operated and controlled components requires electrical power to function properly.
Power for the electronic lock may be provided by batteries, a hard wired connection to a power supply or by any other known power source. Regardless of the source of power, however, there is some risk that it will fail. When the power source of an electronic lock begins to fail, memory storage may become corrupted during any attempt to write to storage, wireless or wired communication may become disrupted, and other electronic lock functions may fail to operate correctly.
Ultimately, in a power fail condition, the lock actuator will be unable to switch between the locked and unlocked state. Accordingly, it is important that the final state of the lock be controlled so that the lock fails to a desired state, with the door either locked or unlocked. Moreover, the lock should fail to a condition that allows it to return to normal operation when power returns. Thus, memory storage functions, remote communication and similar functions should all stop prior to the point that they become unreliable so that the failure occurs to a known state from which normal operation can be resumed when power returns.
In some installations, it is desirable for the lock to fail to the locked state. For example, where the lock is installed at the entrance to a secure room, it is often desirable for the lock to fail so that it continues to prevent unauthorized entry from the exterior side. In this type of installation, the lock mechanism is usually designed to allow an authorized person on the inside to exit the secure area even when the lock has no power. This design maintains security, while preventing people from becoming trapped in an emergency after power has failed.
In other lock installations, it is preferred that the lock fail to the unlocked state. This may facilitate emergency access, prevent people from becoming trapped behind locked doors, etc.
It is an object of the present invention to provide an electronic lock that shuts down to a selected locked or unlocked state when power is lost or voltage is reduced below a minimum operating voltage.
It is another object of the present invention to provide an electronic lock that shuts down to a known state.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification